Thermionic tube



W- L. KRAHL THERMIONIC TUBE Oct. 20, 1931.

Filed June 30, 192 2 Sheets-Sheet l 1/ I II lNVENTOR Mu rE/e L KRAHL e 1; ATTORNEY oct. 20, 1931. w, KRAHL 1,828,537

THERMIONIC TUBE Filed June 30, 1927 2 Sheets-Sheet. 2

lNPl/T P INVENTOR ATTORNEY Patented Oct. 20, 1931 UNITED sTATEs Y PATENT *"OFFICE WALTER LOUIS KRAHL, OI HON'IOLAIB, NEW JERSEY, ASSIGNOR TO ABOTUB'U'S RADIO TUBE COMPANY, 01 HARRISON, NEW JERSEY, A. CORPORATION OF DELAWARE 'rnnamomc TUBE Applicationfiled June so, 1927. Serial No. 202,539.

This invention relates to improvements in vacuum thermionic tubes, adapted for the reception of radio signals, and more particularly to improvements in the cathode struc- 3 ture of such devices. The invention has particular utility in connection with thermionic tubes in which the cathode is energized by the ordinary house-lighting alternating currents.

One of the principal objects of the invention is to provide a tube in which the internal electric circuits connecting the various tube elements to the base terminal pins are reduced to a minimum number, thereby eliminating sources of hum, simpllfylng structural details and improving the over-all efficiency of the unit.

Another object is contemplated in the provision of tube construction in which the junction between the cathode and the heating element for the cathode is formed adjacent that end of the cathode farthest removed from the press or stem of the tube. 7

Further objects of the invention consists in the utilization of the specific cathodeheater connection above mentioned in conjunction with a high resistance and straight filament employed as a heater; in the utilization of a solid metallic cathode tube separated from the heater filament by vacuous space only; in the employment of ion active material on the outer surface of the cathode cylinder intermediate points displaced inwardly from the ends of the tube plate cylinder; and in various other details of construction and methods of manufacture which will appear on consideration of the embodiment of my invention which may be preferred, hereinafter described in detail and illustrated in the accompanying drawings, in which Fig. 1 is a longitudinal sectional elevation of my tube showing the various tube elements and the supporting means and circuits therefor; and

Fig. 2 is a diagrammatic showing of the base and tube elements and the circuits connecting the alternating power source and the input and output units.

Referring to Fig. 1 of the drawings, I have shown a thermionic tube adapted for general radio purposes, including detection and amplification of signals, which is provided with a. glass envelope 10, the up er or top end 11 of which is closed and the ase or lower end 12 of which is formed with a re-entrant portion constituting the stem 13 of the tube. In the upper end of the stem 13 of the tube, known as the press 14, are secured the vari ous support rods for the tube elements. These elements include the cylindrical plate 15, grid 16 and cathode 17. The plate is supported in the press by opposite support rods 18 and 19 which are secured in any suitable manner, as by welding, to the outer plate surface. The grid 16 is supported in the tube by the support rods 20 and 21 on opposite sides of the grid, as clearly shown in Fig. 1.

The cathode 17 is of tubular construction, and preferably of as small a diameter as possible for reasons as will be explained hereinafter. Axially positioned within the cathode tube is the heater filament 25 which is formed preferably of carbon, although any other high resistance material will give satisfactory results. The cathode is of such a length that its ends extend beyond the ends of the cylindrical plate in which it is positioned. To-the lower or base end of the cathode, I apply a band 26, having engaging ends 27 which are connected to support rod 28 extending from within thepress 14. The upper end of the cathode is supported by a clamp 29 which is formed as a collar about the end of the cathode and engages an up-standing support rod 30, the base of the'lower end of which is secured to the press 14. In this manner, the cathode is rigidly supported within the tube. j

The lower end of the heater rod if of carbon, is connected through suitable metallic junction material, such as copper-nickel films,the copper being electro-plated on the carbon, and nickel electroplated on the copper, to the support and connector wire or rod 31. Similarly through a copper-nickel junction, connection to a spring plate 32 is made, the radially extending end of the spring being attached to the end of the support rod 30 so that a complete electric circult is made from the heater support rod 31 through the carbon filament 25, spring 32, and support rod 30, back to the press. The function of the spring 32 is to permit variation in length of the heater filament arising from linear heat expansion and contraction.

The external surface of the cathode wall, well within the area determined by the ends of the plate cylinder, is coated with material capable of high electron emissivity, such as the oxides of strontium and barium, in order to amplify the thermionic capacity of the cathode, in accordance with well-known practice in thermionic tube construction.

Additional rigidity to the supporting means of the various elements are obtained through the utilization of the glass bead applied to the support rod 30, in which are set the reverse-d ends of the plate support rod 19 and grid support rod 20. This connection prevents lateral movement of. the grid and plate adjacent the outer ends thereof. a The lower end of the tube 10 is seated in the cupped base 40 formed preferably of insulating material, such as akelite or hard rubber, and'in the lower end of this base are positioned the four terminal pins 41, 42, 43 and 44. These, pins, since they are of standard design and number, are adapted to fit into any standard type of tube socket, so that the tube is applicable to existing apparatus. The inner or upper ends of the pins are connected within the base and stem to the appropriate terminals of the support rods. The pin 41 is connected to the plate support rod 19 by circuit 45; the pin 42 is connected to the grid support rod 20 by circuit 46; the pin 43 is connected to the heater filament rod 31 by circuit 47; and the pin 44 is connected to the support rod 30 by the circuit 48. It is thus apparent that the internal wiring provides a circuit intermediate the pin 43 through the heater filament 2 5, sprlng 32,

rod 30, wire 48 and pin 44, the cathode 17 having its only connection to the externalcircuit through the clamp arm 29 to the rod 30, and consequently through the connecting wire 48 to pin 44. The upper end of the heater is thus the low potential end, and since the cathode is of relatively large mass, itmay be said with considerable accuracy that the cathode forms an equi-potential surface about the filament.

Reference should now be made to Fig. 2 of the drawings for illustration of a mode of application of the tube to external circuits. A standard type socket is illustrated, having conventional contacts 61, 62, 63, 64, adapte to engage respectively the grid, plate, positive filament, and negative filament leads.

The corresponding leads to the tube elements are diagrammatically indicated in the upper circle including the plate 15, grid 16, cathode tube 17 and heater filament 25. The cathode terminal 44 is connected to the F plus contact of the socket through wire the heater terminal 43 is connected to the negative filament contact 64 by wire 71; the grld terminal 42 is connected to the id contact 61 by wire 72; and the plate term1nal41 is connected to the plate contact 62 by wire 73. Also, the two filament terminals 43 and 44 are connected to the secondary 74 of transformer 75 by wires 76 and 77. The primary 78 of the transformer is connected across the alternating current source 79.

Conventional input and output circuits are illustrated, the input circuit 80 having connection to the grid and the low potential terminal 44 of the cathode heater circuit, and normally including inductance capacity in one or more stages, and negative bias poten tial means, and the output circuit 81 having connection to the plate and to the low potential terminal 44 through the high potential B battery 82, and normally includlng inductances in one or more stages and B potential means.

In order to overcome hum arising from the use of alternating or variable potential current and resulting fluctuations in the value of the electro-magnetic and electro-static otentials within the tube, and particularly etween the cathode and plate, the specific structural elements, as above described, are in general requisite. It is preferable to employ a single, straight filament for heating the cat ode, since by this means the heat energy necessary to bring the cathode into ion emitting condition is considerably reduced. This arises from the fact that as the cathode tube may be fitted closel about the heater filament 25, and since 1: e heat radiation varies with the square of the current, the effectiveness of the heat radiation is considerably increased. This construction is made possible by the use of carbon or similar highly resistant material as it does not require large current flow for a given length to furnish the requisite heat energy. A voltage of 10 to 30 on the heater is used, with a current flow of less than one ampere.

To permit the straight, single filament heater construction, utilization is made of the support rod 30 which also serves as a support for the upper end of the cathode 17 by means of arm 29. The arm 29, in addition to serving as a supporting element, functions also as an electrical connector between the cathode and external circuit. By electrically connecting the upper end of the cathode to the support rod 30, the necessity for employing a circuit connection to the lower end or base of the cathode is eliminated, thus increasing the simplicity of the tube structure.

The eflic'iency of the tube is also augmented by eliminating all solid dielectrics between the heater'filament and the metallic cathode, inasmuch as solids through chemical decomposition and through occluding character- Jim istics,and because ofhe'at la ,serve to destro uniformity of operation an increase the 0 fect of hum due to variable currents in the heater filament.

Increase of efficiency is attained also by the use of a' solid metallic cathode tube of preferably magnetic material, the solid metal of the tube serving as an electro-statlc screen, and the magnetic properties of the metal tending to diminish the electro-magnetic flux variations external to the cathode. The SOlld cathode mass also serves as a heat reservoir to smooth out the fluctuations in heat energy received from the heater filament; also the' metal structure of the cathode permits an effective equality of potential along its length in the tube, whereby its operation is stabllized.

Another feature of the invention is the confinement of the ion-emitting oxides to cathode areas well within the end limits of the plate, so that stray radiation of the electrons is diminished. A factor in the efliciency of the tube also is the extension of the cathode tube at both ends beyond the ends of the plate so that the heater filament, with its relatively higher potentials, is shielded from both the grid and the plate.

Preferably the tube is highly evacuated to increase the uniformity of the electrical performance, both as an amplifier and detector of radio broadcast signals.

In operation, the heater filament is energized by either direct constant, direct fluctuating, or alternating currents. By radiation of energy, which may be partly heat and partly ionic, from the heater to the cathode the coating on the cathode is energized and the tube begins to function. To obtain most effective results where alternating currents are used for heating the cathode, the input and output circuits should be connected to the low potential terminal 44 of the tube, i. e. di-' rectly to the cathode tube 30.

It will be seen that I have provided a tube adapted for use with either alternating or variable potential currents which may be inserted in an ordinary standard tube socket, and in which the internal wiring circuits and tube element supporting means have been simplified to a pronounced degree, thereby securing a highly satisfactory and eflicient instrument for radio signaling purposes.

While I have shown and described a specific embodiment of my invention, it will be understood, of course, that the invention is not confined precisely to the exact disclosure, but to the limits defined by the claims hereto appended.

Having thus described my invention, what I desire to claim is:

1. In a thermionic tube construction, the combination of an envelope; a base having terminal contact pins positioned therein; a-

support stem within the envelope; plate, grid,

and cathode elements havin their lower ends supported on the stem wit in the envelope, sald cathode comprising a metal tube of substantial mass and a single straight heater filament positioned axially within the tube; means for supporting the upper end of said filament, said means being connected to one of said base terminals; and a connection between the upper end of said cathode and said means, said connection forming the support for the upper end of said cathode and the sole connection between said cathode and the heating circuit.

2. In a thermionic tube construction, the combination of an envelope; a base having terminal contact pins positioned therein connected to said envelope; a support stem with in the envelope; plate and grid elements supported within the envelope on said stem; a support rod on said stem; a cathode in the envelope, said cathode being in the form of a tube the lower end of which is attached to the stem, and the upper end of which is attached to said support rod; and a heater filament co-axially positioned within the cathode tube, the upper end of the filament being, resiliently connected to said support rod, there being vacuous space intermediate the heater filament and cathode tube; and electrical connections intermediate the support rod and lower end of the heater filament, respectively, to separate base terminals.

3. In a thermionic tube construction, the combination of an envelope; a base having terminal pins positioned therein connected to said envelope; a support stem within the envelope; anode and control elements within the tube and mounted on said stem; a cathode tube having one end mounted on the stem; a heater filament positioned within the cathode tube; a support rod forming an electrical return circuit for the upper end of the heater filament; a rigid metallic connecting member between said support rod and the free end of said cathode whereby the said end of said cathode is rigidly connected to said support rod and electrically connected tothe filament circuit.

4:. In a thermionic tube construction, the combination of an envelope; a base connected to the envelope; terminal pins mounted in said base; a tubular anode mounted within said envelope; a tubular control element mounted within the anode; a cathode within the control element, said cathode comprising a tubular member and a single, straight heater rod within the tubular member; said member extending beyond the energizable portion of said heater rod and the ends of said anode and control element; electric connections between said anode, control element, and one end of the heater rod and said terminal pins; an electrically conductive support rod extending externally of said anode; and separate supporting and electric connecting members between said sup ort rod and the ends of said heater rod an cathode respectively which are farthest removed from the base whereby the ends of thecathode and heater are rigidly positioned and electrically connected with respect to said support.

5. In a thermionic tube'construction, the combination of an envelope; a base connected .to the envelope; four terminal pins positioned within the base; a tubular anode within the envelope; a tubular control element within the anode; a cathode within the control element, said cathode comprising a tubueam lar member formed of solid metal; a straight heater filament within the member and separated therefrom by vacuous space; connecting members from and PIOVldlllg an electric connection between the end of the cathode member farthest removed. from the base and the corresponding end of the heater said connecting members extending away from both the cathode and heater to reduce heating of said cathode by conduction from said heater; electrical connections from each of said anode and control element to one of said terminal pins; and electrical connections be tween each of said heater filament ends and one of said terminal pins, the circuit connection from the end of the heater farthest removed from the base passing outside of the tubular anode and serving to support both the end of said heater and the end of said gathode member farthest removed from said ase.

6. In a thermionic tube construction, the combination of an envelope; a base connected to the envelope; four terminal pins positioned within the base; a tubular anode within the envelope; a tubular control element within the anode; a cathode within the control element, said cathode comprising a tubular member formed of solid metal; a straight heater filament within the member and separated therefrom by vacuous space; connecting members from and providing an electric connection between 'the end of the cathode member farthest removed from the base and the corresponding end of the heater and serving to space said end of said heater from said cathode; electric connections from each of'said anode and control elements to one of said terminal pins; and electrical connections between each of said heater filament ends and one of said terminal pins the'circuit connection from the end of the heater farthest removed from the base passing outside of the tubular anode.

7. In a thermionic tube construction, the combination of an envelope; a support stem within the envelope; anode and control elements within the tube and mounted on said stem; a cathode having one end mounted from the stem; a heating filament positioned 

